60 BIOLOGY AND TECHNIQUE 



Some of the pigments, like that of Staphylococcus aureus, are probably 

 non-proteid and of a fatty nature.' They are insoluble in water but 

 soluble in alcohol, ether, and chloroform. Because of their probable 

 composition, they have been spoken of as "lipochromes." Other 

 pigments, like the pyocyanin, which lends the green color to cultures 

 of Bacillus pyocyaneus, are water soluble and are probably of proteid 

 composition. Pyocyanin may be crystallized out of aqueous solu- 

 tion in the form of fine needles. The crystals may be redissolved in 

 chloroform. Aqueous solutions retain their color. Solutions in chloro- 

 form, however, are changed gradually to yellow. 



The power of pigment production of various bacteria depends in 

 each case upon cultural conditions. In most cases, this simply signifies 

 that pigment is produced only when the microorganism, finding the most 

 favorable environmental conditions, is enabled to develop all its func- 

 tions to their fullest extent. Thus, a too high acidity or alkalinity of 

 the culture medium may inhibit pigment formation. Oxygen is neces- 

 sary for the production of color in some bacteria, since the bacteria them- 

 selves often produce the pigment only as a leuko-body which is then 

 oxydized into the pigment proper. A notable example of this is the pig- 

 ment of B. pyocyaneus. In other cases, temperature plays an impor- 

 tant r61e in influencing color production. Thus, Bacillus prodigiosus 

 refuses to produce its pigment when growing in the incubator. By 

 persistent cultivation in an unfavorable environment, colored cultures 

 may lose their power of pigment production. 



Sulphur Bacteria. — Wherever the decomposition of organic matter 

 gives rise to the formation of Hj S, in cess-pools, in ditches, at the bottom 

 of the sea, and in stagnant ponds, there is found a curiously interesting 

 group of microorganisms, the so-called sulphur or thiobacteria. Red, 

 purple, and colorless, these bacteria all possess the power of utilizing 

 sulphuretted hydrogen and by its oxidation into free sulphur obtain 

 the energy necessary for their metabolic processes. The colorless sul- 

 phur bacteria, the Beggiatoa and Thiothrices, usually appear as threads 

 or chains which, in media containing sufficient Hj S, are usually well- 

 stccked with minute globules of sulphur. If found upon decomposing 

 organic matter, they often cover this as a grayish mold-like layer. 

 The red sulphur bacteria, of which numerous species have been described 

 by Winogradsky, may appear as actively motile spirilla (Thiospirillum) 

 or as short, thick bacillary forms. 



' Schroeter, Cent. f. Bakt., xviii, 1895. 



